An exemplary conventional read/write head comprises a thin film write element with a bottom pole P1 and a top pole P2. The pole P1 has a pole tip height dimension commonly referenced as “throat height”. In a finished write element, the throat height is measured between the ABS and a zero throat level where the pole tip of the write element transitions to a back region. The ABS is formed by lapping and polishing the pole tip. A pole tip region is defined as the region between the ABS and the zero throat level. Similarly, the pole P2 has a pole tip height dimension commonly referred to as “nose length”. In a finished read/write head, the nose is defined as the region of the pole P2 between the ABS and the “flare position” where the pole tip transitions to a back region.
Pole P1 and pole P2 each have a pole tip located in the pole tip region. The tip regions of pole P1 and pole P2 are separated by a recording gap that is a thin layer of non-magnetic material. During a write operation, the magnetic field generated by pole P1 channels the magnetic flux from pole P1 to pole P2 through an intermediary magnetic disk, thereby causing the digital data to be recorded onto the magnetic disk.
During operation of the magnetic read/write head, the magnetic read/write head portion is typically subjected to various thermal sources that adversely cause ambient and localized heating effects of the read/write head. One such thermal source is attributed to a heat transfer process to the magnetic read/write head from the effect of the spinning magnetic disk.
During a typical operation, the magnetic disk spins at a rapid rate of rotation, typically on the order of several thousands of revolutions per minute (RPM). This rapid rotation generates a source of friction in the ambient air between the ABS and the spinning magnetic disk, thus causing an elevation in the air temperature.
Furthermore, the heating of the motor that drives the magnetic disk causes an additional elevation of the air temperature. In totality, the ambient air temperature may rise from a room temperature of about 25° C. to as high as 85° C. Typically, the read/write head is initially at a room temperature. Consequently, there exists a tendency for a heat transfer process to take place between the ambient air at a higher temperature and the read/write head at lower temperature. The heat transfer causes a rise in the temperature of the read/write head to promote a thermal equalization with the ambient air temperature.
Additionally, the read/write head is also subjected to various sources of power dissipation resulting from the current supplied to the write coils, eddy current in the core, and the current in the read sensor. The power dissipation manifests itself as a localized heating of the read/write head, resulting in a temperature rise similar to the foregoing ambient temperature effect.
The temperature increase of the read/write head further causes a variant temperature distribution as a result of the thermal conduction of diverse materials that compose the read/write head. Typically, most wafer-deposited materials such as those composing the poles P1 and P2 have greater coefficients of thermal expansion (CTE) than that of the substrate. Consequently, the temperature increase effects a general positive displacement of the read/write head as well as a local pole tip protrusion beyond the substrate.
In a static test environment without the effect of the spinning magnetic disk, the localized heating may cause a temperature elevation of as high as 70° C. However, in an operating environment of a magnetic disk drive, the temperature rise resulting from the localized heating may be limited to about 40° C., primarily due to the alleviating effect of a convective heat transfer process induced by the rotating air between the pole tip region and the spinning magnetic disk. The temperature increase associated with the localized heating further promotes an additional protrusion of the pole tip relative to the substrate.
A typical pole tip protrusion in a static environment may be approximately 30 to 35 nm. In an operating environment of a magnetic disk drive, the pole tip protrusion is reduced to a typical value of 7.5 nm to 12 nm. Since a typical flying height is approximately 12.5 nm, the pole tip protrusion associated with thermal heating of the read/write head can cause the read/write head to come into contact with the spinning magnetic disk. While a typical flying height may be about 12.5 nm, there are currently a significant number of low flying heads with flying heights less than 12.5 nm. A steady evolution to lower flying heights exacerbates the problem of physical interference between the pole tip protrusion and the spinning magnetic disk.
This physical interference with the spinning magnetic disk causes both accelerated wear and performance degradation. The wear effect is due to abrasive contact between the slider and the disk. Pulling the softly sprung slider slightly off track impacts the track following capability of the recording device.
In an attempt to resolve the foregoing problem, a number of conventional designs of read/write heads incorporate the use of a material with a coefficient of thermal expansion (CTE) that is lower than that of the substrate. Functionally, the low CTE material is generally used as an insulator between various metals in a conventional magnetic read/write head. An exemplary material used in a conventional magnetic read/write head is silicon oxide, SiO2, which typically has a CTE of 2 parts per million.
In the presence of a temperature rise resulting from a thermal heating of the read/write head, such a material tends to expand at a lower rate than the substrate. This lower expansion rate develops a thermally induced axial restraining force between the material and the substrate. This restraining force effectively reduces the expansion of the substrate, thus mitigating the natural protrusion of the pole tip.
Although this technology has proven to be useful, it would be desirable to present additional improvements. SiO2 has poor thermal conductivity that generally impedes the heat extraction process from the surrounding material to the SiO2 material. Consequently, in spite of the low CTE associated with SiO2, the low thermal conductivity of SiO2 does not sufficiently reduce the temperature rise of the pole tip region and the pole tip protrusion is not adequately reduced with the use of SiO2.
Furthermore, SiO2 lacks elasticity due to its ceramic characteristics. In the presence of the thermally induced axial restraining force, a shear stress is developed at the interface of SiO2 and the surrounding material. This shear stress tends to promote a delamination of the SiO2 material, posing a reliability problem for the read/write head of a conventional design.
In recognition of the issues associated with the use of SiO2 in a conventional read/write head, some alternative materials have been proposed but have not been entirely successfully applied to a read/write head. As an example, while these materials such as Cr, W, possess higher thermal conductivities than SiO2, they are not readily available for deposition and patterning in a read/write head at a wafer-level process.
Thus, there is a need for a read/write head that provides a reduced pole tip protrusion resulting from a thermal heating of the magnetic read/write head during operation. The need for such a design has heretofore remained unsatisfied.